Lets see. Why do I hate Lauren...
First of all, I'm not an S/V shipper. In fact, I can't stand S/V together. So keep in mind that this is not a motivating factor...
I gave the character of Lauren a shot at first, but she never grew on me. The first half of the season she didn't seem very strong to me. When she was "good" she seemed...I don't know...very weak. Next to a character like Sydney (who I'll admit has her 'whiny' moments) she seemed dull and lifeless. All she seemed to say was "stay away from my husband" or the like.
Then all of the sudden she turns evil. Which isn't a bad thing in itself, but I mean, come on...she didn't show any good spy abilities when she was "good" besides that one car chase scene, but even then she wasn't *that* good. Then all of the sudden I'm supposed to believe she's a badass? I don't think so. And now, they've made her character disjointed and there's no continuity whatsoever. It worked with Irina, but this moral ambiguity doens't work for her. First, in Blowback she's all evil and jumping Sark (ick!!
get off my Sarkie) but then in The Frame she gets all upset over killing her father, whom she supposedly hates anyway. But then in Unveiled she's back to being a badass, killing Cipher and torturing the doctor.
No way. Not believable. Not at all. Oh yes, and they have her doing these things that a real double agent would never do. She is calling Sark from the JTF, and in the last episode she's keeps screwing up, but ends up getting lucky in the end...sort of...cause now the CIA is onto her...
Plot holes and character inconsistancy. Thats what I don't like about Lauren.
Edited to Add:
I wanted to add exactly what Joyie said in her post below. When I complain about the accent, the pouty lips, the too much eyeliner...those aren't the reasons I hate her. They are things that annoy me about a character which I hate (for the reasons previously mentioned)
Oh yes, and I think its okay to be against love triangles in general...and thats a valid reason not to like a character. If JJ wanted S/V to have some more obstacles, I really don't think he should have gotten them together so soon...but that's just me...